Fiber protection and power save with security

ABSTRACT

A system and method for Passive Optical Networks (PON) providing integration (cross-correlation) of powersave and fiber protection, optionally with encryption, facilitating the successful operation and/or benefits that can be gained when operating a PON system with these features. A major problem with power save is the detection, since both the OLT and the ONUs rely on a valid signal in order to detect fiber failure. However, the OLT may not detect this for sleeping ONUs, and an ONU in Tx/Rx sleep-mode, may not detect a fiber failure, and may not be aware of the OLTs switchover. In addition to solving the problem of combined fiber protection and power savings, a solution is also needed for providing security for this combination. 
     A current embodiment is a system and method for Passive Optical Networks (PON) providing integration (cross-correlation) of powersave and fiber protection, optionally with encryption.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional patent application(PPA) Ser. No. 61/607,019 filed Mar. 6, 2012 by the present inventors,which is incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to communications, and inparticular, it concerns power saving and fiber protection of networks.

DEFINITIONS

The following terms are generally used in the industry, this document,and/or defined here for clarity. Further definition can be found in thebelow description and/or the applicable industry standard documents.

PON and EPON—a Passive Optical Network (PON) is a network in which userstations are connected to each other by means of a fiber-optical networkthat does not contain any active equipment. The different fibersegments, to which the stations are attached, are coupled together byone or more passive (not electrically powered) optical couplers orsplitters. Optical couplers and splitters are devices that split opticalpower from one fiber into multiple fibers and vice versa. EPON (Ethernetpassive optical network) is the IEEE Ethernet standard for PONs (IEEE802.3ah-2004).

Network configurations—FIG. 4 is a diagram of a first example of aphysical scheme for PON configuration. In the current diagram an opticalline terminal (OLT) OLT1 is the working OLT, OLT2 is the standby OLT. AHOST (generally a CPU management processor) connects to both OLT1 andOLT2, allowing information to pass through the HOST from the working OLT(in this case OLT1) or the standby OLT (in this case OLT2). Working OLT1and standby OLT2 are connected via a SPLITTER to optical networkingunits (ONUs) ONU1, ONU2, ONU3, . . . , ONUN. ONU1 and ONUN are in Tx/Rxsleep-mode (power-save). Note that in Tx/Rx sleep-mode, the ONU may bein sleep-cycle or in awake-cycle. ONU2 is in Tx sleep-mode (either insleep-state or in awake-state). ONU3 is not in sleep-mode (power-save).Tx and Tx/Rx sleep-modes are described below.

FIG. 5 is a diagram of a second example of a physical scheme for PONconfiguration. The network configuration of FIG. 5 is the same asdescribed in reference to FIG. 4. In the current diagram, all ONUs arein power-save either Tx or Tx/Rx. This is a special case of FIG. 4,where if all ONUs are in sleep-cycle then during this time the OLT maynot get any indication of fiber failure.

PowerSave—PowerSave mode is when an ONU enters into a sleep-mode, for acertain amount of time, under certain conditions. Sleeping is usuallydone in cycles. The objectives of power savings modes in EPON are toreduce ecological impact, reduce operating cost, and extend batterybackup time, while minimizing any degradation of network performance.

As shown in FIG. 1, a diagram of sleep and awake-modes of an ONU in aPON, an ONU power save cycle includes sleep-cycle (with typical valuesof 30 ms to 1 s) and awake-cycle (typical values are ˜5-10 ms).

An ONU in power-save (sleep-mode) may be either in Tx sleep-mode, wherethe ONU's receive path is functional all the time and the ONU's transmitpath is functional only during awake-cycle, or in Tx/Rx sleep-mode wherethe ONU's receive path and the ONU's transmit path are functional onlyduring the awake-cycle.

Redundancy—is the duplication of critical components or functions of asystem with the intention of increasing reliability of the system,usually in the case of a backup or fail-safe.

Fiber Protection—(also referred to in the context of this document assimply “protection”) to improve network reliability and survivability,fiber protection switching mechanism can be used in EPON system(includes different redundancy mechanisms). Fiber protection switchingcan be performed by the following two modes:

a) Automatic switching protection: Triggered by PON systemfailure—discovery mechanisms, such as signal loss and signaldegradation, etc.

b) Planned switching: Triggered by management unit uponmanagement/planned events.

Referring to FIG. 1, the relationship between the following modes andcycles can be seen. Note that the loss of signal and switchover timingin the current diagram are for a case of automatic switchover.

Awake-mode: an operating mode of an ONU, in which all of the ONU'ssubsystems in the transmit and receive paths are powered up and fullyfunctional.

Sleep-mode: An operating mode of an ONU, in which some of the ONU'ssubsystems in the transmit (Tx sleep-mode) and transmit and receive(Tx/Rx sleep-mode) path are powered down to save energy. An ONU can bein any combination of the modes. An ONU may also not have a sleep-mode,hence effectively does not have, or go into, a power saving cycle.Includes one or more power-save cycles.

Tx sleep-mode: ONU mode in which only components of the transmit pathpower down (sleep), while the receive path remains fully powered on andsynchronized to downstream data.

Tx/Rx sleep-mode: ONU mode in which components of both the transmit andreceive paths power down (sleep).

Power-save cycle: a period of time including sleep-cycles andawake-cycles.

Sleep-cycle: a period of time in power save cycle during sleep-mode inwhich some of each ONU's subsystems are in sleep-mode. The duration ofthe sleep-cycle is represented as the length of awake-cycle in FIG. 1.

Awake-cycle: a period of time between two consecutive sleep-cycles inwhich an ONU is in awake-mode.

length of sleep-cycle: an amount of time for which an ONU is requestedto enter a sleep-state (sleep-cycle).

length of awake cycle: an amount of time for which an ONU is requestedto enter an awake-state (awake-cycle) and/or the length of time an ONUis awake.

LOSS: Used in the context of this description for convenience to referto a time at which signal is lost (for example, via fiber cut, OLTpower-off, ONU power-off, etc.)

DECLARE: Used in the context of this description for convenience torefer to a time at which loss of signal is declared and the OLT/ONUtransitions to a switchover state. T_(LoS)=DECLARE—LOSS.

SWITCHOVER: Used in the context of the figures for convenience to referto a time at which switchover from a working OLT to a standby OLT isinitiated. T_(switch)=SWITCHOVER—DECLARE. In this context, upon plannedswitchover, DECLARE can be the time that the HOST asked for switchoverfrom the OLT, and not due to LOSS indication)

DEREGISTERED state: if the timestamp drift error is detectedindependently in OLT side or in ONU side, the ONU transitions to theDEREGISTERED state. The ONU needs to complete the registration processfrom discovery gate until1 completion per IEEE 802.3 standards.

DS: Downstream.

HOLDOVER state: EPON devices which support link protection will be inthe HOLDOVER state during the switching time between the working OLT andthe stand-by OLT.

LLID: Logical link identifier.

maximum sleep time of all registered LLIDs: maximum length ofsleep-cycle of all registered ONUs and/or all registered LLIDs.

PCC (PON Cycle Counter): 32 LSB (least significant bits) of the PONcounter, sent as a timestamp from an OLT to ONUs.

PON clock: One of EPON's fundamental parameters is the PON clock. ThePON clock toggles (“clocks”) every 16 nsec (nanoseconds) as per IEEE802.3ah. The OLT and the ONU each have 64-bit counters, known as a “PONcounter”, or in the context of this document simply a “counter”, whichcounts the number of PON clock cycles. An OLT transmits a timestamp(also known as an MPCP timestamp, a 32 bit value of the OLT's PONcounter) in every MPCPDU ((Multi Point Control Protocol Data Unitmanagement frame) that the OLT sends towards the ONUs. The 32 LSBs ofthe PON counter are known as PCC (PON Cycle Counter). The 32 MSBs of thePON counter are known as RCC (round cycle counter). In normal operation,the PON counter of the ONU should match the (master) EON counter of theOLT.

Previous working OLT: OLT in fiber protection, operations of which havebeen taken over by a standby OLT. The previous working OLT is nothandling communication over the network, and the former standby OLT isthe new working OLT.

Power-up: In the context of this document, an alternative reference toan ONU in an awake-mode.

RCC (Round Cycle Counter): 32 MSB (most significant bits) of the PONcounter.

REGISTERED state: an ONU will be in the REGISTERED state while the ONUis registered to an OLT. The ONU will be in the REGISTERED state if thediscovery process between the OLT and the ONU been completedsuccessfully and registration is acknowledged (defined in IEEE 802.3, 64for 1 G-EPON, and 77 for 10 G-EPON).

RTT—round trip time.

Scheme: In the context of this document, generally refers to a method ofPON operation.

SCI: Secure Channel Identifier.

SCI.SA: Source address (MAC address) field of an SCI.

SecTag: Security tag.

Standby OLT: OLT in fiber protection that is not handling communicationover the network and is maintained in the same configuration as theworking OLT.

timestamp: 32 LSB (least significant bits) of the PON counter (PCC),sent as a timestamp from an OLT to ONUs.

T_(LoS): Loss of signal time. Indicates a period of time that has toelapse from a loss of signal before an OLT/ONU transitions to aswitchover state (if the system supports switchover, else the system isbroken and there is no connection between the OLT and ONU until theproblem is fixed), if no REPORT/GATE MPCP has been received.

T_(switch): Switching time or switchover time. Indicates a period oftime that has to elapse after loss of signal (after T_(LoS) has elapsed,when an OLT is in a switchover state), before initiating switchover froma working OLT to a standby OLT.

US: Upstream.

Working OLT: OLT in fiber protection that is handling communication overthe network.

Referring to FIG. 2, a diagram of trunk_1 fiber protection, and FIG. 3,a diagram of trunk_2 fiber protection, there are two generalarchitectures (schemes) for trunk fiber protection. In FIG. 2, exemplarytrunk_1 network configuration includes OLT1 and OLT2 connected inparallel to a SPLITTER, and via the SPLITTER to ONU1, ONU2, ONU3, . . ., ONUN. In FIG. 3, exemplary trunk_2 network configuration is similar totrunk_1, but includes a single OLT having two parallel connections to aSPLITTER, and via the SPLITTER to ONU1, ONU2, ONU3, . . . , ONUN. Intrunk_1 the OLTs are also protected from failure by using at least twoOLTs—a working OLT and one or more (typically one) standby OLT.

Fiber failure—Fiber failure refers to the status of the PON when a fiberneeds to be replaced, either in routine maintenance or because a fiberfailed, and includes three different cases:

1. Manually invoked: if the OLT switchover or fiber repair is manuallyinvoked, then the working OLT must disable the power save to all ONUsand then the fiber protection can start when power save is off. Afterswitchover the power save can get back. Therefore this case is easy tohandle. Referring again to FIG. 4, in a typical case of manually invokedOLT switchover, a HOST notifies all OLTs (in this example OLT1 and OLT2)that a switchover is desired. The working OLT (OLT1) notifies all ONUsto (transition to and) stay in awake-mode, that is, not to entersleep-mode. The working OLT waits a sufficient time for any ONUs thatare in sleep-cycle to transition to awake-cycle, receive notification,and transition to awake-mode. Hence all ONUs are in awake-mode when theswitchover occurs.

2. Automatically invoked (e.g. by an accidental fiber cut). This is thecase dealt with in this document. There are two sub cases:

Tx sleep-mode: the ONU has receive path working while in sleep-cycle.

Tx/Rx sleep-mode: the ONU may have the receive path off while insleep-cycle.

3. Fiber disconnect: after an ONU tries and fails to reconnect from an“Automatically invoked” fiber protection the ONU understands that theONU or the trunk has a fiber cut.

BACKGROUND OF THE INVENTION

Work is currently underway in the area of service interoperability forEthernet passive optical networks (EPON). This work is likely to resultin new standards. Work is being done and definitions being formed in thearea of Optical Link Protection, know as fiber protection or redundancy,and in the area of power save.

A major problem with power save is the detection of fiber failure duringpower save, since both the OLT and the ONUs rely on a valid signal inorder to detect fiber failure. However, the OLT may not detect a validsignal for sleeping ONUs (ONUs in sleep-mode). Correspondingly, an ONUin Tx/Rx sleep-mode may not detect a fiber failure and may not be awareof the OLTs switchover. In addition to solving the problem of combinedfiber protection and power savings, a solution is also needed forproviding this combination when security is enabled.

There is therefore a need to define an integration (cross correlation)of fiber protection, power save, and encryption.

SUMMARY

According to the teachings of the present embodiment there is provided amethod for operating a PON (passive optical network) including at leastone ONU (optical networking unit) and an OLT (optical line terminal),wherein at least one of the at least one ONU is operating in Tx or Tx/Rxpower saving sleep-mode; including the steps of: setting length ofawake-cycle of each ONU to be greater than TLoS (loss of signal time);transitioning said each ONU, upon detecting a fiber failure, switchovernotification, or switchover occurrence: from sleep-mode to awake-mode;and REGISTERED to HOLDOVER state, and setting Tswitch (switchover time)of the OLT to be at least as long as maximum sleep time of allregistered LLIDs.

In an optional embodiment, the method further includes the step of:transmitting, by each ONU, two REPORT packets at each awake-cycle. Inanother optional embodiment, at least one of the at least one ONUcorresponds to a first portion of ONUs corresponding to a first pivotlist of ONUs, further including the step of: configuring, by the OLT,the first portion of ONUs to be in a mode other than Tx/Rx sleep-mode.In another optional embodiment, the PON includes at least two ONUs and asecond portion corresponding to a second pivot list of ONUs includes atleast one of the at least two ONUs other than in the first portion, andthe first portion of ONUS is changed to include at least the secondportion of ONUs. In another optional embodiment, the first pivot list ofONUs is static and transmitted from the OLT to a standby OLT.

In another optional embodiment, the PON includes at least two ONUs,further including the step of: checking, by the OLT, for fiber failurebased on a portion of the at least two ONUs. In another optionalembodiment, the method further includes the step of transmittingrepeatedly until maximum sleep time of all registered LLIDs has passed,by the OLT, SYNC_GATES at a time delta which is less than the ONUs'length of awake-cycle. In another optional embodiment, the methodfurther includes the step of: transmitting repeatedly until maximumsleep time of all registered LLIDs has passed, by the OLT, a wakeupcommand at a time delta which is less than length of awake-cycle.

In another optional embodiment, the OLT includes an OLT RCC (round cyclecounter) and each ONU includes an ONU RCC, the method further includingthe steps of: continuing, at each ONU, normal operation of each of theONU RCC at HOLDOVER state; resetting, at the OLT, OLT RCC uponswitchover if the PON is configured as a trunk_1 architecture; andresetting RCC at each ONU if: each ONU is in HOLDOVER state; switchoverhas occurred within a designated period; and each ONU is unable receivepackets due to decrypter error.

In another optional embodiment, the method further includes the step of:continuing, at the ONUs, to use a previous encryption key for encryptingupstream data, while in HOLDOVER state. In another optional embodiment,the method further includes the steps after a switchover of: setting, atthe OLT and the ONUs, a value of nextPN to be a pre-determined valueless than 0xfff_fff based on a given time; and changing in less than thegiven time, by the OLT, to use new encryption keys.

In another optional embodiment, the pre-determined value is selectedfrom the group consisting of: a. 0xfc0_fff; and a value based on atleast the minimum time required for changing encryption keys.

In another optional embodiment, the method further includes the stepsof: reserving values of nextPN above a pre-determined value, thereserved values to be used during switchover; and setting nextPN, aftera switchover, to one of the reserved values.

In another optional embodiment, the EPON is selected from the groupconsisting of: a 1 G EPON; and a 10 G EPON.

According to the teachings of the present embodiment there is providedan ONU (optical networking unit) operating in Tx or Tx/Rx power savingsleep-mode, the ONU configured: setting an length of awake-cycle greaterthan TLoS (loss of signal time); and transitioning the ONU, upondetecting a fiber failure, switchover notification, or switchoveroccurrence: from sleep-mode to awake-mode; and from REGISTERED toHOLDOVER state.

In an optional embodiment, the ONU is further configured based on aconfiguration selected from the group consisting of: transmitting, byeach ONU, two REPORT packets at each awake-cycle; continue to use aprevious encryption key for encrypting upstream data, while in HOLDOVERstate; and reserve values of nextPN above a pre-determined value, thereserved values to be used during switchover; and setting nextPN, aftera switchover, to one of the reserved values.

According to the teachings of the present embodiment there is provided asystem including: an OLT (optical line terminal) operated based on aconfiguration selected from the group consisting of: setting Tswitch(switchover time) of the OLT to be at least as long as maximum sleeptime of all registered LLIDs; configuring a first portion of one or moreONUs (optical networking units) to be in a mode other than Tx/Rxsleep-mode; checking for fiber failure based on a portion of at leasttwo ONUs, the at least two ONUs operationally connected to the OLT;transmitting, repeatedly until maximum sleep time of all registeredLLIDs has passed, SYNC_GATEs at a time delta which is less than lengthof awake-cycle; transmitting, repeatedly until maximum sleep time of allregistered LLIDs has passed, a wakeup command at a time delta which isless than length of awake-cycle; and reserve values of nextPN above apre-determined value, the reserved values to be used during switchover;and setting nextPN, after a switchover, to one of the reserved values.

According to the teachings of the present embodiment there is provided aPON (passive optical network) system including: at least one ONU(optical networking unit), each ONU configured: setting length ofawake-cycle to be greater than TLoS (loss of signal time); transitioningupon detecting a fiber failure, switchover notification, or switchoveroccurrence: from sleep-mode to awake-mode; and from REGISTERED toHOLDOVER state; and an OLT (optical line terminal) configured: settingTswitch (switchover time) of the OLT to be at least as long as maximumsleep time of all registered LLIDs.

In an optional embodiment, the ONU is further configured based on aconfiguration selected from the group consisting of: transmitting, byeach ONU, two REPORT packets at each awake-cycle; continue to use aprevious encryption key for encrypting upstream data, while in HOLDOVERstate; and reserve values of nextPN above a pre-determined value, thereserved values to be used during switchover; and setting nextPN, aftera switchover, to one of the reserved values, and the OLT (optical lineterminal) is operated based on a configuration selected from the groupconsisting of: setting Tswitch (switchover time) of the OLT to be atleast as long as maximum sleep time of all registered LLIDs; configuringa first portion of one or more ONUs (optical networking units) to be ina mode other than Tx/Rx sleep-mode; checking for fiber failure based ona portion of at least two ONUs, the at least two ONUs operationallyconnected to the OLT; transmitting, repeatedly until maximum sleep timeof all registered LLIDs has passed, SYNC_GATES at a time delta which isless than length of awake-cycle; transmitting, repeatedly until maximumsleep time of all registered LLIDs has passed, a wakeup command at atime delta which is less than length of awake-cycle; and reserve valuesof nextPN above a pre-determined value, the reserved values to be usedduring switchover; and setting nextPN, after a switchover, to one of thereserved values.

BRIEF DESCRIPTION OF FIGURES

The embodiment is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a diagram of sleep and awake-modes of an ONU in a PON.

FIG. 2, a diagram of trunk_1 fiber protection.

FIG. 3, a diagram of trunk_2 fiber protection.

FIG. 4 is a diagram of a first example of a physical scheme for PONconfiguration.

FIG. 5 is a diagram of a second example of a physical scheme for PONconfiguration.

FIG. 6 is an ONU operational state diagram.

FIG. 7 is an ONU switchover state diagram. FIG. 8 is a diagram of ONUstate transitions for solution set #2.

DETAILED DESCRIPTION

As a guide to the reader, an outline of the below description isprovided: Initially, eight problems with implementing powersave andfiber protection are identified. Then an implementation of a firstsolution is described, followed by a description of how this firstsolution is applied to the eight problems. Then an implementation of asecond solution is described, followed by a description of how thissecond solution applies to the eight problems. Following thedescriptions of the first and second solutions, the issue of encryptionis addressed, presenting several problems and then solutions forencryption with powersave and fiber protection.

In recent years, Standards bodies (such as IEEE—The Institute forElectrical and Electronic Engineers), have made progress in the area ofservice interoperability for EPON. The results of the work of theseStandards bodies will provide combined definitions for features of EPONtechnology, that is, EPON powersave, fiber protection, and redundancy.By using the resulting work, service providers will have solutions forproviding beneficial features in EPON systems. While each of thesefeatures (powersave, fiber protection, and encryption) providesbenefits, the integration (cross-correlation) of powersave and fiberprotection, optionally with encryption, has not been defined, thuslimiting the successful operation and/or benefits that can be gainedwhen operating an EPON system with these features.

A current embodiment is a system and method for Passive Optical Networks(PON) providing integration (cross-correlation) of powersave and fiberprotection, optionally with encryption.

4.1 Problem #1—OLT detection: The OLT detects fiber cut by checking theRx path. The OLT does this checking for T_(LoS) duration, to determineif the fiber is non-functional. This is done, for example, by checkingif no REPORT MPCP has been received from any ONU. If this has happened,then a fiber failure is declared and switchover state must be invoked.

However, if some ONUs are now in power-save sleep-cycle then the OLT mayget this indication from a portion of ONUs (that are not in sleep-cycle)but the OLT cannot immediately get this indication from all ONUs.

Tx/Rx sleeping ONUs will not detect and will not respond, Tx sleepingONUs will detect but will not respond.

4.2 Problem #2—Tx ONU switchover while in sleep-cycle: If the PONoperating scheme allows an OLT switchover while some ONUs are inpower-save sleep-cycle, then an ONU which is right now at Tx sleep-cyclemay encounter a new working OLT when the ONU returns to an awake-cycle.However, due to the lack of synchronization of the previous working OLTand the new working OLT, the new working OLT may not know when the ONUsleep-cycle ends and the OLT may not be able to communicate with the ONUafter the ONU transitions to awake-cycle. Further, if informationpassing through the host is slow, or an OLT failure has occurred such asa power failure, then the new working OLT may not know which ONUs arenow in power-save cycle and which ONUs are not in power-save cycle (thatis, in awake-mode).

4.3 Problem #3—Tx/Rx ONU switchover while in sleep-cycle: If the PONoperation (scheme) allows an OLT switchover while some ONUs are inpower-save sleep-cycle then an ONU which is right now at Tx/Rxsleep-cycle (power save mode) may not at all be aware of a switchover.The ONU at Tx/Rx sleep-cycle may wake up for the next awake-cycle to anetwork where a new working OLT is a handling communication over thenetwork, having correspondingly new timestamp and a new OLT MAC address,which should be a reason for an immediate deregistration of the ONUaccording to the protocol. Even more, due to the lack of synchronizationof the previous working OLT and the new working OLT, the new working OLTmay not know when the ONU sleep-cycle ends and the OLT may not be ableto contact the ONU when the ONU transitions to awake-cycle. Even more,if information passing through the host is slow, or an OLT failure hasoccurred such as a power failure, then the new working OLT may not knowwhich ONUs are now in power-save cycle and which ONUs are not in powersave cycle.

4.4 Problem #4—New working OLT transmits a one-time SYNC GATE: In a casewhere the new working OLT transmits a one-time SYNC_GATE, an OLTswitchover can occur while some ONUs are in power-save sleep-cycle. Inthis case, an ONU which is at Tx/Rx sleep-mode when a switchover happensmay miss the SYNC_GATE. The ONU will not be aware of the new timestampand the ONU will probably get deregistered when getting a new timestampfrom the new working OLT.

4.5 Problem #5—New working OLT may not know the wake-up time of sleepingONUs: A problem can arise if a new working OLT does not know the wake-uptime of sleeping ONUs. If the former working OLT and former standby OLTwere aligned in time, or in case of trunk_2 (FIG. 3), this problem doesnot arise with these two OLTs. However, if the two OLTs were not alignedin time (each of the two OLTs having a different timestamp) then theinformation passing between the OLTs through the host cannot include theactual time for each sleeping ONU of when each of the sleeping ONUs willbe in awake-cycle. Thus, the new working OLT will not know when tocontact the sleeping ONUs.

4.6 Problem #6—ONU time for fiber failure detection: A Tx/Rx sleepingONU may have to detect fiber failure during an awake-cycle. The problemis that the period of the awake-cycle can be short (typically net 1 ms(millisecond) of receive time) while the T_(LoS) duration may berelatively long (typically 5 ms). So the amount of time the ONU is inthe awake-cycle may be insufficient to detect fiber failure.

4.7 Problem #7—OLT False fiber failure detection: In order to have astable detection of fiber failure the OLT has to check for a T_(LoS)duration, the time of which is not long compared to the wake-cycle (withtypical values of 5 ms) allowing a loss of some REPORTs where any onereceived REPORT will cause a no fiber failure detection. However, inawake-cycle each ONU transmits only one REPORT so the probability offalse detection grows (probability of detecting a fiber failure wherethere is no actual fiber failure).

An extreme case of false detection would be with two ONUs, one awakewhich has stopped transmitting and one in power-save where a BER of10⁻¹² means a frame error of =1−(1−10⁻¹²)^((64*8)=)5*10⁻¹⁰, so a falsedetection may happen at a probability of 5*10⁻¹⁰ per power-save cycle.

Assuming an awake-cycle every 100 ms then the chance of false detectionbecome 1−(1−5*10⁻¹⁰)^((10*60*60*24))=0.04% for a false fiber failuredetection per one day for one system. This means and a chance of 14% offor a false fiber failure detection per one year for one system.

4.8 Problem #8—Calculation of RTT for all ONUs: There are 4 cases forcalculating an RTT (round trip time) for all ONUs:

1. Both working and standby OLTs have the same RTT. This case presentsno problems for fiber protection with power save.

2. Standby OLT has knowledge of the Standby OLT's RTT (for example, froma trial before the switchover). This case presents no problems for fiberprotection with powersave.

3. Standby OLT knows the RTT of the working OLT for all ONUs. Thispresents a problem, since the new working OLT has to know which ONU isnow in awake-mode in order to check the ONU's RTT.

4. Standby OLT does not know the RTT of the working OLT for all ONUs.This presents a problem, since the new working OLT has to know whichONUs are now in awake-mode in order to check the ONU's RTT.

As described above, there are two general architectures (schemes) fortrunk fiber protection—trunk_1 (FIG. 2) and trunk _2 (FIG. 3). Fromimplementation point of view, trunk_1 is more complicated to implement,whereas the solutions for trunk_1 include the solutions for trunk_2.Therefore for simplicity and clarity of explanation this document willfocus on trunk_1. Based on this description, one skilled in the art willbe able to implement the current invention for trunk_1 and trunk_2.

FIRST EMBODIMENT FIGS. 6-7

6.1 A first embodiment, also known in this document as “solution set #1”is a case where switchover is done when all ONUs are in awake-mode(power-up). When all ONUs are in sleep-cycle then in order to detectfiber failure the OLT must wait until at least some or all of the ONUsare in awake mode. When all ONUs are in sleep-cycle, and synchronizedmode is used, such that all ONUs wake up at the same time, then fiberfailure can only be detected when all ONUs are power-up. Thus theswitchover time (T_(switch)) is extended by (set to a value) up to themaximum sleep time of all registered LLIDs.

When an unplanned switchover occurs, there are two cases:

-   -   1. ONU will stay awake after sleep-cycle (waiting to receive an        OLT frame, after which the ONU will enter again into        sleep-cycle). In this case, a solution is for the ONU to wait.    -   2. ONU will go back to sleep after the awake-cycle. The new OLT        needs to synchronize the sleep cycles. A solution is described        in the paragraph applying solution set #1 to problem #3 (below).

Even if some ONUs are non-sleeping, the user may decide to do switchover“on the safe side” by waiting for a response from all ONUs (by REPORTframe) before allowing the OLT to invoke a switchover.

Solution set #1 facilitates improvements over conventional (existing)power save techniques, including:

In a case where all ONUs are in Tx/Rx sleep-mode and wakeup issynchronized, then this solution set #1 is preferred. In other cases,this solution provides robustness since failure detection is based onall ONUs, and since the switchover is done while all ONUs are inawake-mode (at power-up).

In general, this scheme of solution set #1:

-   -   1. extends switchover (increases switchover time T_(switch)) of        the OLT,    -   2. extends length of awake-cycle of the ONU (less power saving),        and    -   3. changes the power save state transitions to include        transitioning from awake-cycle to awake-mode when detecting        fiber failure.

Note that extending length of awake-cycle may apply to solution set #1for both problems #6 and #7, while extending length of awake-cycle mayapply to solution set #2 for only problem #7.

The following description examines solution set #1 in the context of theabove-described problems #1-6, 8.

6.1.1 Applying solution set #1 to problem #1 (OLT detection), if a nonsynchronized scheme is used then the OLT has to wait for each ONU towake up and transmit a REPORT packet. The amount of time required forwaiting for each ONU to wake up is the maximum sleep time of allregistered LLIDs. Both working OLT and standby OLT should know the valueof maximum sleep time of all registered LLIDs. In the current case, theOLT may have to wait the maximum sleep time of all registered LLIDs, forall ONUs to wake up and transmit a REPORT packet. If a REPORT wasreceived from any of the ONUs, then a fiber failure is not declared.Eventually, an ONU which will not transmit a REPORT for up to MPCPtimeout will become deregistered by the OLT.

In a non-limiting example, in FIG. 1, LOSS (fiber is cut or other issue)happens are the beginning of a sleep-cycle. The OLT waits T_(LoS) andthen at time DECLARE, declares loss of signal and prepares forswitchover from working to standby OLT. After waiting T_(switch)operation of the network switches from the working OLT to the standbyOLT. If Tswitch is less than maximum sleep time of all registered LLIDs,one or more of the ONUs may still be in sleep-cycle when the switchoveroccurs. When the previously sleeping ONU(s) transition to awake-cycle orawake-mode, these ONUs that were sleeping during switchover are now inthe undesirable scenario of having to deal with a new working OLT. Byincreasing the switchover time T_(switch), all ONUs will at least be inawake-cycle and can transition to awake-mode (leaving sleep-mode) asneeded.

If a synchronized sleep scheme is used then the OLT has to wait to thenext common awake-cycle. This may take up to maximum sleep time of allregistered LLIDs. Only at the awake-cycle can the OLT check for fiberfailure.

Note that this scheme requires an increase of the total time of fiberprotection switchover. The increase is by up to maximum sleep time ofall registered LLIDs. If the switching time between working OLT andstand-by OLT is less than or equal to T_(switch) (with typical valuessuch as 50 ms and 150 ms), then T_(switch) will be increased by maximumsleep time of all registered LLIDs (with typical values of 30 ms-1 Sec).

This solution features a change in the regular method of fiberprotection by increasing the switchover time (T_(switch)) up to maximumsleep time of all registered LLIDs in order to handle power saving ONUs.This is non-obvious because normally one would not want to increase theswitchover time in order to avoid affecting the quality-of-service.Longer times between OLTs switchover cause more packets loss. Hence theaccepted practice in the industry is to try to reduce the switchovertime, in contrast to the current embodiment that increases switchovertime.

6.1.2 Applying solution set #1 to problem #2 (Tx ONU switchover while insleep-cycle), Tx-sleeping ONUs can detect fiber failure at any timesince these ONUs receive downstream packets. Once an ONU has detectedfiber failure, the ONU will transition from power-save awake-cycle(awake-state) or from power-save sleep-cycle (sleep state) toawake-mode, and from REGISTERED to HOLDOVER state. These transitions areshown respectively in FIG. 6, an ONU operational state diagram 600, andFIG. 7, an ONU switchover state diagram 700. Arrows 602 and 604 showoperational state transition from respectively awake-cycle andsleep-cycle to awake-mode. Arrow 702 shows switchover state transitionfrom REGISTERED to HOLDOVER. Since the working OLT waits an extendedperiod before declaring fiber failure and initiating a holdover then theOLTs switchover is done while all ONUs are in power-up, so theswitchover becomes a regular switchover scheme.

FIG. 6 shows ONU operational states and transitions 600. An ONU inawake-mode (power-up) can transition to power save cycle and be in anawake-cycle. Conventional transition from the awake-cycle is to asleep-cycle of the power save cycle. As described above, in the currentembodiment the ONU can also transition to awake-mode. From sleep-cyclethe ONU can transition either to awake-mode or start another power savecycle and transition to awake-cycle.

FIG. 7 shows ONU switchover state diagram and transitions 700. An ONU ina DEREGISTERED state can transition to a REGISTERED state. From theREGISTERED state the ONU can transition either to the DEREGISTERED stateor a HOLDOVER state. From the HOLDOVER state the ONU can transitioneither to the DEREGISTERED state or the REGISTERED state. A transitionfrom REGISTERED to HOLDOVER will be establish upon fiber cut or when thehost management implements a planned holdover for maintenance or otherpurposes.

This solution features a change in the regular method of fiberprotection since now ONUs in Tx sleep-mode must exit this state due tofiber failure. This is not obvious since, as this solution is notcurrently being discussed in the field as a possible option and is notdiscussed as part of the power save protocols.

6.1.3 Applying solution set #1 to problem #3 (Tx/Rx ONU switchover whilein sleep-cycle), Tx/Rx-sleeping ONUs can detect fiber failure only whenthe Tx/Rx-sleeping ONU is in an awake-cycle. Since the working OLT waitsan extended period of time (T_(switch)) before declaring fiber failureand initiating a holdover, each of the ONUs has a chance to transitionto awake-cycle (as a normal function of the power save cycle) and detectfiber failure. Once an ONU has detected fiber failure, the ONU willtransition from power-save awake-cycle to awake-mode in the power savestates as shown in FIG. 6 and from REGISTERED to HOLDOVER state in theswitchover states as shown in FIG. 7 above. When the ONU transitions toHOLDOVER state, the ONU can check timestamp and/or OLT MAC address. Ifthe timestamp and/or MAC address needs to be updated, the timestampand/or MAC address on the ONU is updated which indicates that aswitchover has occurred, referred to in the context of this document asa switchover occurrence.

Using this method of ONU operation, the OLTs switchover is done whileall ONUs are in awake-mode, so the switchover becomes a regularswitchover scheme. In other words, as the switchover is done when allONUs are awake, no change is needed to the operation of ONUs, only achange is needed at the OLT to wait an extended period of time beforedeclaring fiber failure. As shown by arrow 700, the ONU will alsotransition from REGISTERED to HOLDOVER state at Tx sleep and Tx/Tx/Rxawake, if detected.

6.1.4 Applying solution set #1 to problem #4 (new working OLT transmitsa one-time SYNC_GATE), since all ONUs are in awake-mode after the OLTsswitchover, this solution solves the problem with the one-timeSYNC_GATE.

6.1.5 Applying solution set #1 to problem #5 (new working OLT may notknow the wake-up time of sleeping ONUs), Since all ONUs are inawake-mode after the OLTs switchover, this solution solves the problemof a new working OLT not knowing the wake-up time of ONUs in sleep-cycle(sleeping ONUs).

6.1.6 Applying solution set #1 to problem #6 (ONU time for fiber failuredetection), A

Tx/Rx sleeping ONU may have to detect fiber failure during anawake-cycle. The problem is that the period of the awake-cycle (lengthof awake-cycle) is short (typically net 1 ms of receive time) while theT_(LoS) duration may be relatively long (typically 5 ms).

Two solutions include extending the length of awake-cycle and decreasingthe T_(LoS) duration. Decreasing the T_(LoS) may be problematic sincethis increases the probability of false fiber failure detection by theONU. On the other hand, increasing the length of awake-cycle to begreater than T_(LoS) will result in more power consumption. Given thecost/benefit of these two solutions, a preferred implementation is toonly set (increase) the length of awake-cycle to be greater thanT_(LoS).

This solution features a change in the regular method of power savesince this solution increases the length of awake-cycle. This solutionis not obvious since one would not want to increase the length ofawake-cycle since this causes a somewhat lowering of the overall powersaving,

6.1.7 Applying solution set #1 to problem #8 (Calculation of RTT for allONUs), since all ONUs are in awake-mode, this case is handled in thesame manner as for regular fiber protection using solution #1.

6.1.9 In summary, solution set #1 features changes to the conventional(existing standard) power-save scheme including:

1. ONU at Tx sleep-mode: when detecting a fiber failure transitions toawake-mode (power-up/exits power save cycle). In other words, when anONU is in Tx sleep-mode, the ONU's receiver is awake, so the ONU candetect a fiber failure. When the ONU detects a fiber failure, the ONU“powers-up”, transitioning to awake-mode. Refer to the description aboveof applying solution set #1 to problem #2 (Tx ONU switchover while insleep-cycle).

2. ONU at Tx/Rx sleep-mode: when detecting a fiber failure or switchovernotification during an awake-cycle, transitions directly from theawake-cycle to awake-mode (without re-entering a sleep-cycle). As duringTx/Rx sleep-mode both the ONUs transmit and receive paths are powereddown, the ONU cannot detect a fiber failure during sleep-cycle. However,as the OLT is changed to wait an extended prior of time before declaringfiber failure, the ONU has time to (transition to awake-cycle) wake upthe ONUs Rx path and detect fiber failure. Refer to the descriptionabove of applying solution set #1 to problem #3 (Tx/Rx ONU switchoverwhile in sleep-cycle).

3. ONU at Tx/Rx sleep-mode: set (extend) length of awake-cycle to begreater than T_(LoS). Refer to the description above of applyingsolution set #1 to problem #6 (ONU time for fiber failure detection).

4. ONU: Optional implementation of a solution at the ONU to handle falsefailure detection, as described below in the section “applying solutionset #1 and #2 to problem #7”.

5. OLT: increasing by up to maximum sleep time of all registered LLIDsthe switching time (T_(switch)) the OLT waits before declaring fiberfailure and initiating a holdover. Refer to the description above ofapplying solution set #1 to problem #1 (OLT detection).

6.1.10 In summary, solution set #1 features changes to conventional(existing standard) fiber protection scheme including:

1. OLT: Set (extend) switchover time T_(switch) to be equal to or longerthan maximum sleep time of all registered LLIDs. Refer to thedescription above of applying solution set #1 to problem #1 (OLTdetection).

2. ONU: At Tx/Rx sleep-mode: check for a switchover state afterawake-cycle, and if fiber failure, transition from power-saveawake-cycle to awake-mode and from REGISTERED to HOLDOVER state. Referto the description above of applying solution set #1 to problem #3(Tx/Rx ONU switchover while in sleep-cycle).

3. OLT: Handling ONUS at Tx/Rx sleep-mode: Set (extend) length ofawake-cycle to be greater than T_(LoS). Refer to the description aboveof applying solution set #1 to problem #6 (ONU time for fiber failuredetection).

For completeness, note that OLT: at manually invoked fiber protection,delays to insure that all ONUs are in awake-mode (not in sleep-mode)before initiating switchover. See description above related to the caseof manually invoked fiber failure.

SECOND EMBODIMENT FIG. 8

6.2 If not all ONUs are in sleep-cycle, the user may choose to allow theOLT to detect fiber failure based on some (a portion of) non-responsiveONUs. This assumes that some ONUs is sufficient for detecting fiberfailure.

In an extreme case even if one ONU is “important” (high service levelagreement—SLA) and is non-sleeping and all the rest are non-important(low SLA) then fiber failure detection for this one important ONU maycause a fiber failure detection and an OLT switchover. Otherwise, anyalgorithm can be used to do switchover based on detection of majority ofONUs or a combination of majority and priority of ONUs. In anon-limiting example algorithm, if two or more ONUs of high-priority orfour or more ONUs of any priority have not transmitted REPORT duringT_(LoS), then the OLT declares fiber failure.

The following description examines a second implementation, also knownin this document as solution set #2, to problems #1-6, 8-9 above, in thecontext of the previous assumption.

Solution set #2 facilitates improvements over conventional (existing)power save techniques, including:

A. Solution set #2 overcomes less-desirable operating issues of solutionset #1, as described below.

B. Solution set #2 allows a switchover without checking all ONUs, thus afaulty switchover may happen (although the chance can be relativelyextremely low if a few ONUs are awake). Solution set #2 is more complexthan solution set #1, so care should be taken to avoid implementationerrors.

C. If all ONUs are in sleeping in Tx/Rx sleep-mode or Tx sleep-modewithout early wake up, then solution set #2 can be used as a hybridsolution by waiting for some ONUs to wake up, if some ONUs have a lowvalue length of sleep-cycle.

6.2.1 Applying solution set #2 to problem #1 (OLT detection), sincedetection is based only on awake ONUs (ONUs in awake-mode) then a changein fiber failure detection includes detecting based a portion of theONUs, as decided by the user. Based on this description, one skilled inthe art will be able to implement a detection algorithm appropriate fora specific application.

There are four kinds of ONUs, in other words, ONUs in four states ofoperation:

-   -   1. Tx/Rx—an ONU in the Tx/Rx sleep-mode cannot respond to        communications from an OLT, as both the receive path and the        transmit path are powered-down.    -   2. Tx without early wakeup: The working OLT does not know if the        ONUs have:        -   A. encountered fiber failure and cannot respond due to the            fiber failure, or        -   B. if the ONUs do not respond since although there is no            problem as far as these ONUs know, the transmit path is            powered down in Tx sleep-mode.    -   3. Tx with early wakeup: The working OLT transmits a wakeup        signal to all ONUs, and the ONUs with early wakeup capability        transition to awake-mode. Now these ONUs in awake-mode can be        used for supporting the probability of correct detection of        fiber failure. When the OLT detects fiber failure in some        awake-mode (power-up) ONUs, the OLT may send a wakeup signal to        ONUs in the Tx sleep-mode which support early-wakeup, in order        to increase probability of the OLT fiber failure detection.    -   4. Awake-mode (power-up/non power save) ONUs: these ONUs in        awake-mode can be used for detecting fiber failure.

6.2.2 Applying solution set #2 to problem #2 (Tx ONU switchover while insleep-cycle), the same scheme is used as described above in reference toapplying solution set #1 to problem #2

6.2.3 Applying solution set #2 to problem #3 (Tx/Rx ONU switchover whilein sleep-cycle), an OLT switchover may have happened while an ONU was inpower-save sleep-cycle. In this case the ONU will wake up at the nextawake-cycle without knowing that an OLT switchover has happened. Therewill now be two problems: the new working OLT has a (1) new timestampand (2) a new OLT MAC address.

Therefore the ONU, waking up from sleep-cycle, has to assume that aswitchover has occurred. The transition from REGISTERED to HOLDOVERstate happens at every transition from sleep-cycle (power save sleepstate). As shown in FIG. 8, a diagram of ONU state transitions forsolution set #2, in ONU operational state diagram 600, when the ONUtransitions from sleep-cycle to awake-cycle or to awake-mod; in the ONUswitchover state diagram 700, the ONU transitions from REGISTERED toHOLDOVER state, as indicated respectively by arrows 802 and 804. The ONUwill exit HOLDOVER state once the ONU receives from an OLT a SYNC_GATEor any later GATE. Note that an ONU that is still in sleep-mode, whentransitioning to an awake-state (as opposed to being at the end of asleep-mode and transitioning from sleep-cycle to awake-mode) does notknow if a switchover has occurred, so will wait to receive a GATE from aworking OLT. If the working OLT is the same working OLT as before theONU went into sleep-cycle, the ONU can continue to work as configured(for example, continuing in sleep-mode by transitioning to anothersleep-cycle). If the working OLT is a new OLT, the ONU will transitionto awake-mode.

In the awake-cycle, the ONU may detect a switchover occurrence, that is,that a switchover has been done, by various conditions, including:

1. Updated OLT MAC Address.

2. Updated time stamp.

When detecting a switchover, the ONU will transition from awake-cycle toawake-mode (power-up state) in the ONU operational state diagram (alsoknown as ONU power saving state machine).

If the ONU has recognized an updated timestamp, an updated OLT MACaddress, or another indication/condition that there is a new OLT, theONU will stop the power save cycle and transition to awake-mode(power-up) state.

This solution features a change in the regular method of power savesince now ONUs in Tx/Rx sleep-mode must go to HOLDOVER state after everywake up. This is non-obvious, since the fiber protection protocol looksorthogonal to the power save protocol so one would not expect the powersave protocol to cause a change in fiber protection protocol. In otherwords, conventional power save protocol is unrelated to protectionprotocol in the existing standards.

6.2.4 Applying solution set #2 to problem #4 (new working OLT transmitsa one-time SYNC_GATE), if a switchover has happened while a Tx/Rx ONUwas in sleep-cycle then the ONU may miss the SYNC_GATE and have a wrongtimestamp.

A solution is that the new working OLT will repeatedly transmitSYNC_GATEs as long as maximum sleep time of all registered LLIDs has notpassed. The SYNC_GATEs must be transmitted at a time delta which issmaller than the ONUs' length of awake-cycle in order to make sure thatthe ONUs will recognize the SYNC_GATE. Delaying the transmission ofSYNC_GATE by maximum sleep time of all registered LLIDs has no advantageover the solution set #1 and is therefore not recommended. Transmissionof SYNC_GATES includes transmission of broadcast SYNC_GATES anddiscovery SYNC_GATES.

The SYNC_GATE may be transmitted as a broadcast packet using the IEEE802.3

Discovery packet. This will allow all 1 G-ETON-Security encrypted ONUsto synchronize. This may also save the need of transmitting a GATE foreach ONU.

This solution features a change in the regular method of fiberprotection since now the OLT has to transmit SYNC_GATE multiple times.This repeated transmission seems non-intuitive when talking about onlyfiber protection. Also, this repeated transmission is not needed ifsolution set #1 is chosen for implementation. Also, transmitting abroadcast SYNC_GATE or a Discovery packet as a SYNC_GATE is not theregular method of choice.

An alternative approach is to not transmit SYNC_GATE at all if theSYNC_GATE is not required. This is based on the fact that each ONU willeventually get a GATE for transmitting REPORT and maybe data.

62.5 A. 0 in solution set #1 to problem #5 (new working OLT may not knowthe wake-up time of sleeping ONUs), if a switchover has happened while aTx/Rx ONU was in sleep-cycle then the new working OLT may not know whenthe sleeping ONU will wake up. Therefore the OLT needs to wake up theONU, and then have the ONU re-enter power save, if appropriate for eachawakened ONU. As for Tx sleeping ONUs, these ONUs are already power-upsince these ONUs have detected fiber failure.

The new working OLT must also transmit a wakeup command to all Tx/RxONUs as long as maximum sleep time of all registered LLIDs has notpassed. The wakeup must be transmitted at a time delta which is smallerthan the ONUs length of awake-cycle in order to make sure that the ONUwill recognize the wakeup. Typically, a wakeup command is implemented bythe transmission of a wakeup packet. Transmission of wakeup packets caninclude transmission of broadcast wakeup packets.

After the ONU has transitioned to awake-mode, then if suitable, thewhole process of power saving will start automatically at a normalmanner with the new working OLT.

The wakeup command may be transmitted from the OLT as a broadcastpacket.

The wakeup command and the SYNC_GATE command have different purposes andmust both be transmitted. There is no importance as to which command isfirst.

Delaying the transmission of wakeup by maximum sleep time of allregistered LLIDs has no advantage over the solution set #1 and istherefore not recommended.

This solution features a change in the regular method of fiberprotection since now the OLT has to transmit the wakeup command multipletimes, while this seems non-intuitive when talking about only fiberprotection. Also, repeated transmission is not needed if solution set #1is chosen for implementation. Also, transmitting a broadcast wakeup isnot the regular method of choice.

6.2.6 Applying solution set #2 to problem #6 (ONU time for fiber failuredetection), since a Tx/Rx sleeping ONU does not have to detect fiberfailure then there is no issue with the time that the ONU takes todetect fiber failure.

6.2.7 Applying solution set #2 to problem #8 (Calculation of RTT for allONUs), for two cases where:

1. either the OLTs (working and standby) share the same RTT values,

2. or the standby OLT already knows the RTT map,

there is no problem (#8, calculation of RTT for all ONU's).

3. For a case where a new working OLT has the RTT map of the previousworking OLT, then the new working OLT must find the RTT of only one ONU.Using the new RTT from this one ONU and the known old RTT from this ONU,the OLT can calculate a difference between the new RTT and the old RTT,and the add/subtract that difference from the other ONUs' RTTs, thussaving the need and the time for finding (receiving) the RTT from theother ONUs. An exemplary algorithm for finding this one ONU is asfollows:

-   -   A. Start with a first set of all ONUs which have the minimum        value of length of sleep-cycle, referred to as        sleep_time_level1.    -   B. For this first set of ONUs, choose any one ONU, if RTT can be        found for this one ONU, then done.    -   C. else choose another ONU from the first set,    -   D. repeat until sleep_time_level1 expires and all ONUs of this        group have been tried    -   E. If RTT is still not found, repeat the above using a second        set of ONUs which have a next minimum level of length of        sleep-cycle.

4. Always synchronize the RTT map from the working OLT to the standbyOLT, to avoid a case where the standby OLT does not have any working OLTRTT map.

Alternatively, in order to avoid using solution set #1 (which has aslower switchover), the working OLT must always keep N ONUs (where N isan integer number) known as pivot ONUs, or a list of pivot ONUs) ateither non-power-save or at Tx sleep-mode. The list of these pivot ONUscan be static. Information regarding pivot ONUs can be passed to thestandby OLT, so that when the standby OLT becomes the new working OLT,the standby OLT can refer to any of these N pivot ONUs as a known basefor RTT calculating. N may be any number with typical values of one ortwo. Even if the information of which ONUs are non power saving or at Txsleep-mode has not passed to the new working OLT, if the new working OLTknows that there are N ONUs like this then the search algorithm willreveal fast results. The use of Tx sleep-mode is based on the fact thatsuch an ONU will wake up when detecting fiber failure.

An alternative description of the above PON includes configuring the PONwith at least one ONU and at least one OLT. In the case where a portionof the ONUs is static, in other words the pivot list, or identity of aportion of the ONU's is static, the PON can be configured with more thanone (a plurality) on ONUs, to provide a first portion first pivot list)and second portion (second pivot list). The PON architecture can beconfigured in a configuration including either trunk_1 or trunk_2.

This solution features a change in the regular power save method sincethis solution requires some ONUs to not be in Tx/Rx sleep-mode. This isnot obvious since this solution increases the overall system powerconsumption, which is contrary to the general goal of power savings inthe system.

6.2.9 In summary, solution set #2 features changes to conventional(existing standard) power-save scheme including:

1. ONU at Tx sleep-mode: when detecting a fiber failure transition toawake-mode (power-up / exits power save cycle). Refer to the descriptionabove of applying solution set #2 to problem. #2 (Tx ONU switchoverwhile in sleep-cycle).

2. ONU at Tx/Rx sleep-mode: invoke a HOLDOVER state after every powersave wake up (every change from sleep-cycle to awake-cycle or toawake-mode). Refer to the description above of applying solution set #2to problem #3 (Tx/Rx ONU switchover while in sleep-cycle),

3. Optional implementation of requiring some ONUs to not be in Tx/Rxsleep-mode. Refer to the description above of applying solution set #2to problem #8 (Calculation of RTT for all ONUs),

4. ONU: Optional implementation of a solution at the ONU to handle falsefailure detection, as described below in the section “applying solutionset #1 and #2 to problem #7”.

6.2.10 In summary, solution set #2 features changes to conventional(existing standard) fiber protection scheme including:

1. OLT: Check for fiber failure based on some ONUs. Refer to thedescription above of applying solution set #2 to problem #1 (OLTdetection).

2. ONU: ONUs in Tx/Rx sleep-mode must go to HOLDOVER state after everywake up. Refer to the description above of applying solution set #2 toproblem #3 (Tx/Rx ONU switchover while in sleep-cycle).

3. OLT: New working OLT repeatedly transmits SYNC_GATEs at a time deltawhich is less than the ONUs' length of awake-cycle and as long asmaximum sleep time of all registered LLIDs has not passed. Refer to thedescription above of applying solution set #2 to problem #4 (new workingOLT transmits a one-time SYNC_GATE).

4. OLT: New working OLT transmits repeatedly a wakeup command to allTx/Rx ONUs at a time delta which is smaller than the ONUs length ofawake-cycle and as long as maximum sleep time of all registered LLIDshas not passed. Refer to the description above of applying solution set#1 to problem #5 (new working OLT may not know the wake-up time ofsleeping ONUs).

For completeness, note that OLT: at manually invoked fiber protection,delays to insure that all ONUs are in awake-mode (not in sleep-mode)before initiating switchover. See description above related to the caseof manually invoked fiber failure.

6.3 Applying solution set #1, and #2 to problem #7 (false failuredetection), false OLT fiber failure detection has a low probability asdescribed above in reference to problem #7—OLT false fiber failuredetection.

Options for handling false failure detection include:

1. Ignore this problem. The probability of this problem is low, and thepenalty of an un-needed switchover is low, although there will be sometraffic loss.

2. Changing operation of the ONU to transmit two REPORT packets at eachawake-cycle. This may extend the awake-cycle by a DBA cycle (typical by0.5 ms), thus adding minor power consumption to the power consumption ofconventional operation.

An example of conventional power consumption:

-   -   Awake_cycle_orig=2 ms    -   Sleep_cycle=98 ms    -   DBA_Cycle is 0.5 ms    -   Power_saving_orig=98/(98+2)=98%

An example of power consumption when transmitting two REPORTs:

-   -   Awake_cycle=2.5 ms    -   Sleep_cycle=97.5 ms    -   DBA_Cycle is 0.5 ms    -   Power_saving_orig=97.5/(97.5+2.5)=97.5%

This solution for OLT false fiber failure detection features a change inthe conventional power save protocol that is not obvious, as inconventional protocols there is no need for two or more REPORTs, andadding REPORTS increases the power consumption of the PON system.

THIRD EMBODIMENT

6.4 In a system where the above innovative power save and fiberprotection schemes have been implemented, an embodiment described belowcan be used to provide encryption compatible with the combined fiberprotection and power savings, in other words defining an integration(cross correlation) of fiber protection, power save, and encryption.Note that the term “encryption” is generally used below in the generalsense of including both encryption and decryption.

6.4.1 As a guide to the reader, there are currently three popular modesof encryption in use and/or being developed. The below descriptionincludes non-limiting examples of the current embodiment in the contextof each of these three modes of encryption:

A. 1 G-EPON-SECURITY RCC. Unique, as this mode uses timestamp from anOLT with RCC from an ONU. (Refer to problems #9, # 10, below.)

B. CTC Triple Churn (3churn) for 1 G/10 G. This method of encryptionwill continue to work with the above embodiments for power save andfiber protection. (No changes necessary).

C. 802.1AE (standard-based encryption for 10 G). Requires OLT.SA (OLTsource address/MAC address) to be known to the OLT and ONU. (Refer toproblems #11, #12, below.)

6.4.2.1 Problem #9—1 G-EPON-SECURITY RCC: This mode of encryption uses atimestamp (PCC, 32 LSB of OLT PON counter) from an OLT with RCC (32 MSBof ONU PON counter) from an ONU as an input for the encryption blockengine. The timestamp is 32 bits which has a wraparound about every 67seconds. The PCC (time stamp) will be synchronized between the OLT andthe ONU, when the ONU receives broadcast MPCP message (like Discoveryframe) or Sync frame. RCC enhances the timestamp to 64 bits which has awraparound time which is much larger than a man's lifetime. As the RCCis not transmitted in the packets from the OLT to the ONU, the RCC onthe OLT needs to be synchronized with the RCC on the ONU for successfulencryption (encryption and decryption).

A problem with this mode of encryption is that after a switchover, thecounter of the new working OLT and ONU are normally not synchronized, sothe OLT and ONU are not able to successfully encrypt nor decryptpackets.

In addition, there is a question about Tx/Rx sleep-mode in solution set#2 where switchover can happen without the ONU being aware that a newOLT is now the working OLT. Hence, the new working OLT has a differentcounter and will transmit timestamps that are not consistent with thepreviously received timestamps from the previous working OLT.

6.4.2.2 Solution #9 (solution to problem #9):

For a system using a trunk architecture there is only one OLT, so thereis no need to reset the RCC, and problem #9 is avoided.

For a system using a trunk_1 architecture, there are two OLTs. AtHOLDOVER state, the RCC of an ONU will be reset. The new working OLTmust start a new encryption session, thus the counters (RCCs) of the newworking OLT will be reset (get cleared). [As a note, for completeness,in order for the standby OLT (previously working OLT) to start a newencryption session, the standby OLT must stop the old/previousencryption operation in order to allow a new encryption session when thestandby OLT switches over to become a working OLT.] In general, when anOLT starts encrypted communications with a corresponding ONU, the OLT'sRCC counter is reset, the OLT sends a timestamp to the ONU for PCCsynchronization, and the ONU's RCC counter is reset.

In order to provide automatic fiber protection in this mode, preferablythe ONU does not know if the ONU is part of a trunk_1 or trunk_2architecture. This can be accomplished by configuring the ONU asfollows:

9.1. The ONU initially assumes trunk_2 architecture and continuing(maintaining) normal operation of the RCC (does not reset the RCC) atHOLDOVER state.

9.2. The OLT knows if trunk_2 or trunk_1 is being used. In trunk_1 uponswitchover, the OLT will reset the counter (RCC) as explained above.

9.3 On the ONU, if a switchover has recently occurred (for example inthe last 500 ms) and the ONU has not been able to receive any packetsdue to decrypter error, then the ONU knows that a trunk_1 architectureis being used, and the counter on the ONU is reset (resets the ONU'sRCC). Now the OLT and the ONU are both using reset counters, the RCCsare synchronized and the OLT and ONU will be able to successfullyencrypt.

Regarding Tx/Rx sleep-mode in solution set #2 and a switchover hashappened without the ONU knowing, then the ONU will not be able toreceive any packets due to decrypter error. Thus, a decryption errorwill cause the ONU to transition from power-save sleep-cycle (sleepstate) to awake-mode, from REGISTERED to HOLDOVER state, and then resetthe RCC (counter on the ONU). This solution is consistent with theabove-described solutions for solution set #2. When not in Tx/Rxsleep-mode, the ONU will receive a wakeup command from the OLT, togetherwith decryption errors, will cause an RCC reset.

This solution features a change in the regular 1 G-EPON-security methodsince now if the ONU recognizes decryption errors, the ONU resets theRCC. This is non-obvious.

6.4.3.1 Problem #10—Upstream encryption. In normal operation, an OLTsends a key to an ONU to use for the ONU to use for decryptingdownstream data and encrypting upstream data. The ONU is capable ofsupporting both previous (old) and current (new) encryption keys soafter switchover the new working OLT can use the previous key forencrypting downstream data (since the ONU has not yet been sent the newdecryption key). However, a problem remains in the upstream, that is,what key does the ONU use for encrypting upstream data?

For completeness, the Tx/Rx sleep-mode in solution set #2 needs to alsobe considered, specifically if there will be a problem with the ONUsleeping during switchover.

6.4.3.2 Solution #10 (solution to problem #10): After being in theHOLDOVER state, the ONU should always use the previous key forencrypting upstream data, until a new key is received.

For Tx/Rx sleep-mode in solution set #2, when exiting sleep-cycle theONU will recognize decrypter errors, and then transition from REGISTEREDto HOLDOVER state. After holdover the previous key will be used forupstream encryption. Otherwise, at Tx/Rx if a real switchover hashappened the ONU will get a SYNC_GATE (with a new OLT MAC address) or awakeup, recognize a new OLT and will know that a switchover hashappened, and then the previous key will be used.

While similar conventional techniques exist for downstream decryption,conventional teachings have not considered using these techniques tosolve the problem of upstream encryption. Using the current method forupstream encryption is an innovative solution to this upstreamencryption problem.

6.4.4.1 Problem #11—802.1AE Short SecTag: For 802.1AE with short SecTagthere is a need to have a pre-shared index (called SCI). The SCI is anindex to the secure channel, a 64-bit index, and is built as follows:

-   -   48-bit OLT MAC Address (OLT.SA)    -   16-bit LLID (with MSB=‘0’)

After switchover there is a new OLT with a new MAC address. A problem isthat the ONU now has to learn the new OLTs SA (source address) aftereach switchover before the ONU can start decrypting. This is problematicfor solution set #2 where the ONU assumes a holdover at every wakeupfrom Tx/Rx.

In other words, the fact that there is a new working OLT means thatfiber protection occurred and there was a switchover. However, the ONUis still configured to operate with the old OLT. In this case, how areencryption keys handled?

6.4.4.2 Solution #11. According to the 802.1AE specification, there isno requirement to have the same SCI for the OLT and the ONU when workingwith short SecTag. In other words, the SCI is optional and not neededwhen using short SecTag. So, at the OLT there is a short SecTag indexcalled ‘2’ or ‘3’, but this index is an index to the special case of the“no index”. The same is true for the ONU. Thus, in fact, there is noneed to have the same index on both the OLT and ONU for successfuldecryption at the ONU.

So, a new working OLT will have a new SCI for the short SecTag. The newworking OLT will use a most recently updated key at the OLT which is theONU's current key or the previous key. The ONU can support both keys,indexed by the 2-bit AN (Association Number) parameter which is explicitalso at short SecTag. In other words when a PON system is implementedusing power save and fiber protection according to the abovedescription, encryption according to 802.1AE can be used without furthermodification to the above described solution set #1 and #2.

6.4.5.1 Problem #12—802.1AE replay protect: The optional replay protectis a counter which advances for each packet. However, the standby OLT isnot aware of the current value of this counter, so after a switchover,decryption will fail.

6.4.5.2 Solution #12. A solution to the 802.1AE replay protect problemcan include the following:

12.1 Step 1. The nextPN value for replay protect may always increase upto the limit of 0xffff_ffff. There is an assumption that the new key(after OLT switchover) always gives sufficient time for replacing keysbefore getting near the 0xffff_ffff value. Thus, the new working OLTshould change the nextPN to a value near 0xffff_ffff and afterwards thenew working OLT should change the SA (keys and nextPN) as soon aspossible. The same method should be used on the ONU (change the nextPNto a value near 0xffff_ffff).

Typical values for replay protect include: 100 ms for changing the keys,which is ˜2M packets (of 64 B) at 10 G rate which is 2̂21, so change(jump) the nextPN to 0xffc0_(—)0000.

Note that this solution also works for Tx/Rx sleep-mode with solutionset #2.

12.2 Step 2. DS (downstream) and US (upstream) keys in working operationshould be changed before nextPN reaches 0xffc0_(—)0000 and DS and USkeys must be changed within 100 ms from switchover.

An alternative description of the current solution is to reserve valuesof nextPN above a pre-determined value. The reserved values will be usedduring switchover. After switchover, setting nextPN to one of thereserved values.

This solution includes a new method of handling the replay protect withfiber protection switchover, using the non-intuitive fact that thenextPN is not a rolling counter, so the transmitter can increase thenextPN as much as the transmitter wants.

As can be seen from the above description, using the Standard's set ofdefinitions of each area in EPON does not provide a complete solution tosimultaneous operation of various beneficial features of the EPON. Whena user (service provider, system vendor, or chipset vendor) requiresmaximum benefits from the EPON system, the user needs a combination ofdefinitions that work with all of the beneficial features together as asystem. The above embodiments include innovative solutions forsimultaneously operating of features (powersave, protection, andencryption) and gaining benefit from each one of these features, whilepreserving the Standard's definitions.

Note that a variety of implementations for modules and processing arepossible, depending on the application. Modules are preferablyimplemented in software, but can also be implemented in hardware andfirmware, on a single processor or distributed processors, at one ormore locations. The above-described module functions can be combined andimplemented as fewer modules or separated into sub-functions andimplemented as a larger number of modules. Based on the abovedescription, one skilled in the art will be able to design animplementation for a specific application.

The use of simplified calculations to assist in the description of thisembodiment does not detract from the utility and basic advantages of theinvention.

It should be noted that the above-described examples, numbers used, andexemplary calculations are to assist in the description of thisembodiment. Inadvertent typographical and mathematical errors do notdetract from the utility and basic advantages of the invention.

It will be appreciated that the above descriptions are intended only toserve as examples, and that many other embodiments are possible withinthe scope of the present invention as defined in the appended claims.

What is claimed is:
 1. A method for operating a PON (passive opticalnetwork) including at least one ONU (optical networking unit) and an OLT(optical line terminal), wherein at least one of the at least one ONU isoperating in Tx or Tx/Rx power saving sleep-mode; in an awake-mode eachONU's subsystems in transmit and receive paths are powered up andfunctional; in a sleep-mode some of each ONU's subsystems in transmit(Tx sleep-mode) and transmit and receive (Tx/Rx sleep-mode) path can bepowered down; sleep-cycle is a period of time during sleep-mode in whichsome of each ONU's subsystems are powered down; awake-cycle is a periodof time during sleep-mode between sleep-cycles; length of awake-cycle isan amount of time for which each ONU is requested to enter anawake-cycle; loss of signal time (T_(LoS)) is a period of time that hasto elapse from a loss of signal before the OLT or each ONU transitionsto a switchover state; switchover time (T_(switch)) is a period of timethat has to elapse after loss of signal before the OLT initiatesswitchover to a standby OLT; and maximum sleep time of all registeredLLIDs is a maximum length of sleep-cycle of each registered ONU,comprising the steps of: a. setting length of awake-cycle of each ONU tobe greater than T_(LoS) (loss of signal time); b. transitioning saideach ONU, upon detecting a fiber failure, switchover notification, orswitchover occurrence: i. from sleep-mode to awake-mode; and ii. fromREGISTERED to HOLDOVER state, and c. setting T_(switch) (switchovertime) of the OLT to be at least as long as maximum sleep time of allregistered LLIDs.
 2. The method of claim 1 further comprising the stepof: d. transmitting, by each ONU, two REPORT packets at eachawake-cycle.
 3. The method of claim 1 wherein at least one of the atleast one ONU corresponds to a first portion of ONUs corresponding to afirst pivot list of ONUs, further comprising the step of: d.configuring, by the OLT, said first portion of ONUS to be in a modeother than Tx/Rx sleep-mode.
 4. The method of claim 3 wherein the PONincludes at least two ONUs and a second portion corresponding to asecond pivot list of ONUs includes at least one of the at least two ONUsother than in said first portion, and said first portion of ONUs ischanged to include at least said second portion of ONUs.
 5. The methodof claim 3 wherein said first pivot list of ONUs is static andtransmitted from the OLT to a standby OLT.
 6. The method of claim 1wherein the PON includes at least two ONUs, further comprising the stepof: d. checking, by the OLT, for fiber failure based on a portion of theat least two ONUs.
 7. The method of claim 1 further comprising the stepof: d. transmitting repeatedly until maximum sleep time of allregistered LLIDs has passed, by the OLT, SYNC_GATES at a time deltawhich is less than each ONU's length of awake-cycle.
 8. The method ofclaim 1 further comprising the step of: d. transmitting repeatedly untilmaximum sleep time of all registered LLIDs has passed, by the OLT, awakeup command at a time delta which is less than each ONU's length ofawake-cycle.
 9. The method of claim 1 wherein the OLT includes an OLTRCC (round cycle counter) and each GNU includes an GNU RCC, furthercomprising the steps of: d. continuing, at each GNU, normal operation ofeach of the ONU RCC at HOLDOVER state; e. resetting, at the OLT, OLT RCCupon switchover if the PON is configured as a trunk 1 architecture; andf. resetting RCC at each ONU if i. each ONU is in HOLDOVER state; ii.switchover has occurred within a designated period; and iii. each ONU isunable receive packets due to decrypter error.
 10. The method of claim 1further comprising the step of: d. continuing, at the ONUs, to use aprevious encryption key for encrypting upstream data, while in HOLDOVERstate.
 11. The method of claim 1 further comprising the steps after aswitchover of: d. setting, at the OLT and the ONUs, a value of nextPN tobe a pre-determined value less than 0xfff_fff based on a given time; ande. changing in less than said given time, by the OLT, to use newencryption keys. The method of claim I wherein said pre-determined valueis selected from the group consisting of: a. 0xfc0_fff; and b. a valuebased on at least the minimum time required for changing encryptionkeys.
 12. The method of claim 1 further comprising the steps of: d.reserving values of nextPN above a pre-determined value, the reservedvalues to be used during switchover; and e. setting nextPN, after aswitchover, to one of the reserved values.
 13. The method of claim 1wherein said EPON is selected from the group consisting of: a. a 1 GEPON; and b. a 100 EPON.
 14. A system comprising: a. an ONU (opticalnetworking unit) operating in Tx or Tx/Rx power saving sleep-mode, saidONU configured: i. setting an length of awake-cycle greater than T_(LoS)(loss of signal time); and ii. transitioning said ONU, upon detecting afiber failure, switchover notification, or switchover occurrence: A.from sleep-mode to awake-mode; and B. from REGISTERED to HOLDOVER state.15. The system of claim 14 wherein said ONU is further configured basedon a configuration selected from the group consisting of: a.transmitting, by each ONU, two REPORT packets at each awake-cycle; b.continue to use a previous encryption key for encrypting upstream data,while in HOLDOVER state; and c. reserve values of nextPN above apre-determined value, the reserved values to be used during switchover;and setting nextPN, after a switchover, to one of the reserved values.16. A system comprising: a. an OLT (_(optical) line terminal) operatedbased on a configuration selected from the group consisting of: i.setting T_(switch) (switchover time) of the OLT to be at least as longas maximum sleep time of all registered LLIDs; ii. configuring a firstportion of one or more ONUs (optical networking units) to be in a modeother than Tx/Rx sleep-mode; iii. checking for fiber failure based on aportion of at least two ONUs, said at least two ONUs operationallyconnected to said OLT; iv. transmitting, repeatedly until maximum sleeptime of all registered LLIDs has passed, SYNC_GATES at a time deltawhich is less than each of one or more ONUs' length of awake-cycle; v.transmitting, repeatedly until maximum sleep time of all registeredLLIDs has passed, a wakeup command at a time delta which is less thaneach of one or more ONUs' length of awake-cycle; and vi. reserve valuesof nextPN above a pre-determined value, the reserved values to be usedduring switchover; and setting nextPN, after a switchover, to one of thereserved values.
 17. A PON (passive optical network) system comprising:a. at least one ONU (optical networking unit), each ONU configured: i.setting length of awake-cycle to be greater than T_(LoS) (loss of signaltime); ii. transitioning upon detecting a fiber failure, switchovernotification, or switchover occurrence: A. from sleep-mode toawake-mode; and B. from REGISTERED to HOLDOVER state; and b. an OLT(optical line terminal) configured: i. setting T_(switch) (switchovertime) of the OLT to be at least as long as maximum sleep time of allregistered LLIDs.
 18. The system of claim 17 wherein a. said ONU isfurther configured based on a configuration selected from the groupconsisting of: i. transmitting, by each ONU, two REPORT packets at eachawake-cycle; ii. continue to use a previous encryption key forencrypting upstream data, while in HOLDOVER state; and iii. reservevalues of nextPN above a pre-determined value, the reserved values to beused during switchover; and setting nextPN, after a switchover, to oneof the reserved values, and b. said OLT (optical line terminal) isoperated based on a configuration selected from the group consisting of:i. setting T_(switch) (switchover time) of the OLT to be at least aslong as maximum sleep time of all registered LLIDs; ii. configuring afirst portion of one or more ONUs (optical networking units) to be in amode other than Tx/Rx sleep-mode; iii. checking for fiber failure basedon a portion of at least two ONUs, said at least two ONUs operationallyconnected to said OLT; iv. transmitting, repeatedly until maximum sleeptime of all registered LLIDs has passed, SYNC_GATES at a time deltawhich is less than length of awake-cycle; v. transmitting, repeatedlyuntil maximum sleep time of all registered LLIDs has passed, a wakeupcommand at a time delta which is less than each of one or more ONUs'length of awake-cycle; and vi. reserve values of nextPN above apre-determined value, the reserved values to be used during switchover;and setting nextPN, after a switchover, to one of the reserved values.